Photoelectric sensor and method of detecting an object to be detected using the same

Abstract

A photoelectric sensor has a light emitting section, a light receiving section, an amplification circuit for amplifying an electric signal from the light receiving section, an A/D converter for converting an output voltage of the amplification circuit into a digital value, and a processing section for controlling the light emitting operation and processing the digital value provided by the A/D converter. In a high-precision mode, the processing section causes the light emitting section to perform the light emitting operation a plurality of times successively, adds a plurality of digital values provided by the A/D converter in response to the light emitting operation performed plurality of times, and processes the digital value of the addition result as a detection value corresponding to the light receiving amount.

What is claimed is:  
     
       1. A photoelectric sensor comprising: 
       a light emitting section for emitting light to a detection area;  
       a light receiving section for receiving light from the detection area;  
       an amplification circuit for amplifying an electric signal corresponding to a light receiving amount output from said light receiving section;  
       an A/D converter for converting an output voltage of said amplification circuit into a digital value; and  
       a processing section for controlling light emitting operation of said light emitting section and processing the digital value provided by said A/D converter,  
       wherein said photoelectric sensor has a high-precision mode wherein a light emitting amount of said light emitting section or an amplification ratio of said amplification circuit is made lower than that in a normal mode, whereby said amplification circuit or said A/D converter is made hard to be saturated, and wherein the processing section, in the high-precision mode, causes said light emitting section to perform the light emitting operation a plurality of times successively, adds a plurality of digital values provided by said A/D converter in response to the light emitting operation performed plurality of times, and processes the digital value of the addition result as a detection value corresponding to the light receiving amount.  
     
     
       2. The photoelectric sensor as claimed in  claim 1 , further comprising: 
       a display comprising a first display section and a second display section, each consisting of a plurality of digit places, being placed side by side,  
       wherein said processing section displays the detection value in the first display section and uses the second display section to display any other than the detection value in the normal mode and uses the first and second display sections to display the detection value with an increased number of digit places in the high-precision mode.  
     
     
       3. The photoelectric sensor as claimed in  claim 1 , wherein in the high-precision mode, said processing section sets a threshold value and a shift amount based on the detection value under a predetermined condition, decrements the shift amount from the threshold value and the detection value to provide a threshold value and a detection value with as many digits as reduced to the maximum number of display digits of the detection value in the normal mode, and displays the threshold value and the detection value from each which the shift amount is decremented on a display as a threshold value and a detection value for display. 
     
     
       4. The photoelectric sensor as claimed in  claim 3 , further comprising: 
       a display comprising a first display section and a second display section, each consisting of a plurality of digit places, being placed side by side,  
       wherein said processing section is responsive to a switch signal input for switching a display mode between a first display mode of using both the first and second display sections to display the detection value with an increased number of digit places and a second display mode of using only either of the first and second display sections to display the detection value for display with a reduced number of digit places.  
     
     
       5. A photoelectric sensor comprising: 
       a light emitting section for emitting light to a detection area;  
       a light receiving section for receiving light from the detection area;  
       an amplification circuit for amplifying an electric signal corresponding to a light receiving amount output from said light receiving section;  
       an A/D converter for converting an output voltage of said amplification circuit into a digital value; and  
       a processing section for controlling light emitting operation of said light emitting section and processing the digital value provided by said A/D converter,  
       wherein said photoelectric sensor has a high-precision mode wherein a light emitting amount of said light emitting section or an amplification ratio of said amplification circuit is made lower than that in a normal mode, so that said amplification circuit or said A/D converter is not saturated, and wherein the processing section, in the high-precision mode, causes said light emitting section to perform the light emitting operation a plurality of times successively, averages a plurality of digital values provided by said A/D converter in response to the light emitting operation performed plurality of times, and processes the average digital value as a detection value corresponding to the light receiving amount.  
     
     
       6. A photoelectric sensor comprising: 
       a light emitting section for emitting light to a detection area;  
       a light receiving section for receiving light from the detection area;  
       an amplification circuit for amplifying an electric signal corresponding to a light receiving amount output from said light receiving section;  
       an A/D converter for converting an output voltage of said amplification circuit into a digital value; and  
       a processing section for controlling light emitting operation of said light emitting section and processing the digital value provided by said A/D converter,  
       wherein said photoelectric sensor has a high-precision mode wherein a light emitting amount of said light emitting section or an amplification ratio of said amplification circuit is made lower than that in a normal mode, so that said amplification circuit or said A/D converter is not saturated, and wherein the processing section, in the high-precision mode, adds the digital value provided by said A/D converter a plurality of times or multiplies the digital value by an integer to find a value, and processes the found value as a detection value corresponding to the light receiving amount.  
     
     
       7. A method of detecting an object to be detected using a photoelectric sensor, in a high-precision mode wherein a light emitting amount or an amplification ratio of an electric signal corresponding to a light receiving amount is made lower than that in a normal mode, the method comprising: 
       performing, a plurality of times successively, a light emitting operation of emitting light to a detection area with the light emitting amount;  
       performing, in response to the light emitting operation performed plurality of times, a light receiving operation of receiving light from the detection area, a amplification operation of amplifying the electric signal corresponding to the light receiving amount of the received light with the amplification ratio, and a converting operation of converting an output voltage of the amplified electric signal into a digital value, so as to provide a plurality of digital values in response to the light emitting operation performed plurality of times; and  
       adding the plurality of digital values provided in response to the light emitting operation performed plurality of times; and  
       processing the digital value of the addition result as a detection value corresponding to the light receiving amount.  
     
     
       8. The method of detecting an object to be detected using a photoelectric sensor as claimed in  claim 7 , further comprising: 
       setting a threshold value and a shift amount based on the detection value;  
       decrementing the shift amount from the threshold value and the detection value to provide a threshold value and a detection value with as many digits as reduced to the maximum number of display digits of the detection value in the normal mode; and  
       displaying the threshold value and the detection value from each which the shift amount is decremented on the display as a threshold value and a detection value for display.  
     
     
       9. A photoelectric sensor having a light emitting section for emitting light to a detection area, a light receiving section for receiving light from the detection area, an amplification circuit for amplifying an electric signal corresponding to a light receiving amount output from said light receiving section, an A/D converter for converting an output voltage of said amplification circuit into a digital value and a processing section for controlling light emitting operation of said light emitting section and processing the digital value provided by said A/D converter, said photoelectric sensor comprising: 
       a normal mode having either a predetermined light emitting amount emitted by said light emitting section or a predetermined amplification ratio of said amplification circuit;  
       a high-precision mode having either lower light emitting amount emitted by said light emitting section than said predetermined light emitting amount in said normal mode or lower amplification ratio of said amplification circuit than said predetermined amplification ratio of said amplification circuit in said normal mode to be made harder saturation condition of said light receiving amount of said light receiving section;  
       a switching means for switching between said normal and high-precision modes;  
       a display section for displaying a numeral with a first predetermined digit number based on said processed digital value of said processing section in said normal mode and a numeral with a second predetermined digit number which is larger than said first predetermined digit number in said normal mode, based on said processed digital value of said processing section in said high-precision mode,  
       wherein when said high precision mode is selected by said switching means, said processing section causes said light emitting section to perform the light emitting operation a plurality of times successively, adds a plurality of digital values provided by said A/D converter in response to the light emitting operation performed plurality of times, processes the digital value corresponding to the added plurality of digital values as a detection value corresponding to the light receiving amount and causes said display section to display a numeral corresponding to the processed digital number in said high-precision mode.  
     
     
       10. The photoelectric sensor as claimed in  claim 9 , wherein said display section comprises a first display section and a second display section, each consisting of a plurality of digit places, being placed side by side, and wherein said processing section displays the detection value in the first display section and uses the second display section to display any other than the detection value in the normal mode, and uses the first and second display sections to display the detection value with an increased number of digit places in the high-precision mode. 
     
     
       11. The photoelectric sensor as claimed in  claim 9 , wherein in the high-precision mode, said processing section sets a threshold value and a shift amount based on the detection value under a predetermined condition, decrements the shift amount from the threshold value and the detection value to provide a threshold value and a detection value with as many digits as reduced to the maximum number of display digits of the detection value in the normal mode, and displays the threshold value and the detection value from each which the shift amount is decremented on the display section as a threshold value and a detection value for display. 
     
     
       12. The photoelectric sensor as claimed in  claim 11 , wherein said display section comprises a first display section and a second display section, each consisting of a plurality of digit places, being placed side by side, and wherein said processing section is responsive to a switch signal input for switching a display mode between a first display mode of using both the first and second display sections to display the detection value with an increased number of digit places and a second display mode of using only either of the first and second display sections to display the detection value for display with a reduced number of digit places.